Braun tube



Aug. 9, 1938. K. SCHLESINGER 2,126,286

BRAUN TUBE Filed June 11, 1954 2 Sheets-Sheet 1 Ur: uenioc:

Aug. 9, 1938. K. SCHLESINGER 2,126,286

BRAUN TUBE Filed June 11, 1934 2 Sheets-Sheet 2 I w B Patented Aug. 9,1938 PATENT OFFICE BRAUN TUBE Kurt Schlesinger, Berlin, Germany,assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz,Germany Application June 11, 1934, Serial No. 730,111 Germany June 10,1933 16 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0.G.

The object of the invention is a Braun tube, operated under high vacuum,with electrostatic concentration of the ray. I

According to the invention, the stream of elec- 5 trons is controlled inits intensity, preferably by space charge control, and by the use ofsuitable electrostatic fields or if desired also by the use ofintermediate diaphragms, is preliminarily concentrated and projected onto a diaphragm. The aperture of this diaphragm, in accordance with theinvention, is reproduced on the luminous screen of the Braun tube bymeans of an electron-optical system of constant focus.

Since the aperture in the diaphragm acts as surface of constant form andsize but varying light intensity, it is possible in this fashion toproduce image points, which are not dependent on their intensity asregards form and size, and in consequence also remain unaltered when achange-over takes place from lightest white to darkest black.

The diaphragm aperture to be reproduced on the luminous screen, the formof which aperture 25 determines the form of the image point, isconveniently made as small as possible (for example,

less than 1 mm.), and may be furnished with a rectangular, hexagonal orother suitable form. In order to avoid a thermal overloading of thisdiaphragm, the preliminary concentration device is constructed'in suchfashion that the greatest preliminary concentration takes place when theintensity of the ray is at its maximum.

35 The diaphragm itself is preferably made of a good heat-conductivematerial with the highest possible fusing point, which material at thesame time enables the diaphragm aperture to be furnished with a veryexact form (clean-cut edges).

40 According to the invention, the diaphragm may conveniently consist oftwo parts, viz., a supporting ring composed of a suitable material, suchas copper, and a diaphragm portion connected with this supporting ringand furnished with the aper- 5 ture, said portion consisting of asuitable material,

such as tungsten, tantalum or molybdenum.

As electron-optical system (electron lens) there are employed inaccordance with the invention preferably systems which are constructedin such 50 fashion that the speed of the ray when passing through thesame remains unaltered, or practically unaltered.

It is particularly convenient to employ systems which comprisefundamentally two positively 55 biassed electrodes, between which thereis located a negatively biassed electrode of suitable form. The lensitself producing the optical efiect according to the invention thenconsists practically of the negative element and one of the saidpositive elements, the braking fleldextending 5 mainly between those twoelectrodes. The second positive electrode allows of adjusting the focusof the system without changing the speed which the electrons have beforethey enter the system. Therefore this -third electrode is practi- 1ocally of a great value but is not necessary as to the reproducingfunction of the system.

In this connection the positive electrodes may conveniently beconstructed in the form of annular plates having aperture of the orderof, for 16 example, approximately 5 mm., and if desired united by meansof a metallic cylinder to form a sleeve, in'the interior of which thereisprovlded the negatively biassed electrode.

The negative electrode, in accordance with the 20 invention, may beconstructed, for example, in the form of a funnel-shaped electrode, thediameter of the smaller funnel preferably being approximately equal tothe diameter of the openings of the positive electrode.

It is particularly convenient to make the negative electrode in the formof annular electrode with short set-on metallic cylinder. In thisconnection the diameter of the annular plate aperture will preferably bemade almost as large as the diameter of the apertures in the positiveelectrode, for example of the order of approximately 5 mm. On the otherhand the set-on metallic cylinder lsfurnished with a diameter ofapproximately twice the size.

It is also possible to employ as negative field generator an annularplate composed of insulating material, which is furnished on the oneside with a spiral coating of a semi-conductive substance (for example,a highly ohmic spiral composed of graphite or colloidal carbon) thecommencing point of the spiral situated adjacent the aperture beingconnected with a suitable positive potential and the end point thereofwith a suitable negative potential, so that the potential decreases inproportion to the spacing from the centre point.

According to one feature of the invention the spacing of the negativeelectrode from the positive electrode directed towards the tube cathodeis made as small as possible, so that a braking field of any appreciablekind is not formed between these two electrodes.

The two positive electrodes of the system are connected with each other,and may conveniently positive electrode on the cathode side, theelectron-optical system acts in exactly the same mannor as an opticalcollecting lens.

Accordingly when using a system of this nature the size of the imagepoint with given size of the aperture in the diaphragm is determined bythe ratio between the distance of the diaphragm to be reproduced fromthe electron-optical system and the distance of the electron-opticalsystem 4 from the image screen.

Since on the one hand it is impossible in practice to make the diaphragmaperture too small and on the other hand, for technical reasons, theimage point may not exceed a certain size, which is dependent on thesize of the image and the number of lines, the diaphragm, the opening ofwhich is to be reproduced, is arranged, according to the invention, asfar as possible from a practical point of view away from theelectron-optical system.

A distance of approximately 6-8 cm., which with a length of bulbamounting to, say, 30 cm. cqrresponds with an approximately fourfold orfivefold enlargement, has been found to be fully sufilcient in practice.

According to the invention, the space between I the diaphragm and theelectron-optical system with the positive electrodes of theelectron-optical system.

If in contradistinction to the arrangement above described the negativeelectrode of the electron-optical system is disposed in such fashionthat the smaller aperture thereof (small funnel aperture or cylinderholding plate) is directed towards the positive electrode on the imagescreen side, the electron-optical system corresponds fully in itsproperties with an optical dispersing lens.

According to another feature of the invention it is now quite readilypossible by the use of dispersing lenses of this nature, or by thecombination of electron-optical dispersing and collecting lenses, oralso by the combination of collecting lenses of different focus (i. e.,electronoptical systems, the negative electrodes of which are biassed todifferent extents whilst the positive electrodes possess the samepotential) to conduct systems, which do not produce magnified images ofthe diaphragm aperture, but project the same on to the image screen innatural size or on a reduced scale.

Since the electron-optical collecting and dispersing lenses correspondfundamentally with the optical arrangements, it is possible to assembledifierent systems of this nature according to the principles well knownin the optical art.

-The use of combined systems of this charac- 75 ter is of considerableimportance according to the invention insofar as the same also allow ofthe production of the smallest image points with compact assembly of thesystem.

According to a further feature-of the invention it is possible toproduce images with a small sur-: face, i. e., images of that nature,the diagonals of which do not difieii appreciably from the diameter ofthe neck of the tube in which the parts of the system are arranged. Inthis connection the diameter of the tube may conveniently be selected upto approximately 10-15 cm.

By reason of this dimensioning of the image it is possible to make thedistance of the deflecting systems from the image screen comparativelysmall. f

Thus, the electron-optical system may be arranged in such fashion thatits spacing from the image screen is considerably less than its distancefrom the diaphragm to be reproduced, so that the latter may bereproduced on the image screen even on a reduced scale.

The image produced in this fashion may then be reproduced on a desiredscale of enlargement by suitable optical means. According to anadditional form of embodiment of the invention the path of the raywithin the neck 'of the tube may be multiplied by a single or multipledeviation of the ray.

In this manner it is also possible in direct fashion to producetelevision images of large size with small image points withoutnecessity for increasing the length of the tube.

The deviation of the ray may preferably be caused by the use of magneticfields.

The image point distribution may conveniently be performed by the use ofpairs of deflecting plates having the deflecting plates disposed intitled relation to each other in the manner known per se. To avoidcross-current error the plates may be negatively biassed in relation tothe ray,

Between the deflecting plates and the image screen there may be providedin accordance with the invention a preferably large-surface interceptingelectrode, which is maintained at a potential that is positive inrelation to the positive electrodes of the electron-optical system, andserves to intercept the return-flow electrons and to prevent the samefrom penetrating into the neck of the bulb containing the parts of thesystem.

On the inside of the wall of the tube there may be provided a metalliccoating, which commences at approximately the level of the interceptingelectrode and extends at least 8-12 cm. into the bulb of the tube.

In order to produce bright and at the same time comparatively smallimage points, it may be convenient to illuminate the diaphragma'perture, which is to be reproduced, by means of a bundle of electronsdirected as far as possible parallel, i. e., to pre-concentrate the raypreferably in such fashion that the electrons proceed-- ing from thecathode enter as far as practically possible parallel into the aperturein the diaphragm.

According to a further feature of the invention, there are providedbetween the cathode and the diaphragm to be reproduced concentratingmeans which may consist of two electron-optical systems, of which theone functions preferably as collecting lens and the other as dispersinglens.

-The electron-optical systems may each consist, in the manner set forthabove, of one or two eleelement. The operation of the electron-opticalsystem (i. e., the action as collecting or dispersing lens) isdetermined solely by the extent and nature of the bias of thisintermediate element in relation to the outer elements. There may besaid generally that completely similar electron-optical systems may beemployed for the preliminary concentration of the ray andfor thereproduction of the anode aperture on the screen.

Some forms of embodiment of the tube according to the invention and alsocertain details are illustrated by way of example in the drawings inwhich a Fig. 1 shows the most elementary form of the total arrangementwith a simple electron-optical system of the collecting lens type,whilst in Fig. 2 there is shown a form of embodiment of the anode, in

Figs. 3 and 4 two different types of electronoptical collecting lenses,and in Fig. 5 an electron-optical dispersing lens.

Fig. 6 shows a spiral semi-conductor electrode according to theinvention, whilst Fig. 7 illustrates the combination of two of theseelectrodes to form a preliminary concentration system.

Fig. 8 shows a Braun tube according to the invention havingpre-concentrating means of another type.

Fig. 9 shows an arrangement with single deviation of the ray, and

Fig. 10a detail of the arrangement illustrated in Fig 9, whilst in Fig.11 there is'indicated an arrangement with double deviation of the ray.

The combination of a plurality of electronoptical collecting orcollecting and dispersing systems accordingto the invention has not beenparticularly shown, as these difl'erent combinations may be readilyobtained from the stated the preliminary concentration element, i thedia- Y phragm, which at the same time may be used as the anode, 5 thescreening cylinder, i I the electron-optical system with the positiveelectrodes 6 and 8 and the electrode 7, which is furnished with anegative bias in relation thereto (for example, of approximately 200-500volts), 9 and iii are the two pairs of deflecting plates, i2 is theintercepting electrode, l3 the metallic wall coating, and it theluminous screen.

All of the electrodes are preferably connected to form a system by theuse of insulating holding means. The anode s, the cylinder 5 and theplate electrodes 6 and 7 may be conductively connected with each other,and. if desired the electrodes 6 and 1 supplemented to form a cylinder.The length of the cylinder 5 may be selected up to'approximately 15 cm.A dimensioning of this kind enables points to be produced or a sizenecessary for large-size television images with a simpleelectron-optical collecting system.

As shown in Fig. 2, the anode 4 may conveniently consist of a holdingring I5 of suitable material, such as copper, which carries the smallplate i6 having the diaphragm aperture 41, this plate consisting, forexample, of tantalum. In order to .avoid or reduce as far as possiblethe occurrence of secondary electrons, the part of the anode directedtowards the cathode may conveniently be sooted. Further, the anode ispreferably linked up with a potential as high as possible.

Fig. 3 shows an electron-opticaTcollecting lens system, in which thenegative electrode is constructed in funnel-like form. According to theinvention, the distance of the two funnel apertures from the positiveelectrodes is preferably made as small as possible, approximately 1 mm.or less.

In the system illustrated in Fig. 4 the negative electrode consists ofthe holding plate l9 and the set-on cylinder Hi, the diameter of whichmay conveniently amount to twice the diameter of the opening of theholding plate.

If, as shown in Fig. 5, the negative electrode is arranged in suchfashion that the larger aperture thereof is directed towards thepositive plate on the cathode side, the electron-optical system is ableto act, as a dispersing lens.

In Fig. 6:

is an insulating plate with the aperture 22, on which there is providedthe spiral 2i consisting of a semi-conductive material. The commencingpoint 24 of the spiral is connected with a positive potential (forexample, the anode potential) and the end of the spiral 23 with asuitable negative potential.

Fig. '7 shows a system consisting of two electrodes 'of this nature,which system may be employed, for example, as preliminary concentrationsystem.

The intermediate electrode in the electron-optical system according tothe invention requires to be furnished with merely a weak negative bias,for example to the extent of 200-500 volts, in relation to the outerelectrodes. Since this negative bias determines the focus of the system,the same should be selected in individual cases with consideration tothe specific data of the tube.

The tube according to the invention may be operated with the relativelylow anode potentials (for example, 1000-3000 volts) usual in the case ofgas tubes. Thus, for example, it is possible to impart to the anode ofthe tube a potential of merely approximately 1000-1500 volts, and ifdesired to employ the wall coating as after-acceleration anode.

It is, however, also possible to impart to the metallic wall coating apotential which is negative as compared with the intercepting electrodeprovided according to the invention, and in this manner to effectafter-concentration in the space of the bulb.

In Fig. 8:

i is the cathode with the emissive surface 25, 2 the Wehnelt cylinderwith the control plate 26, 25 an electron-optical system acting ascollecting lens, and 33 an electron-optical system acting as dispersinglens, whilst H is the electron-optical system which reproduces thediaphragm opening 21 on the image screen. The system 29 consists of thetwo (preferably earthed) plates 28 and 3|, which are raised to anodepotential, and the cylinder 30 which is arranged between the same andpossesses a comparatively strong negative bias (for example 400 volts)in relation to the plates 28 and 3|. 34 is the wall of the tube.

The potentials of the system I l, i. e. the potentials applied to theplates 6 .and 8 and the inner element 1 may correspond with thepotentials of the system 29.

In contradis'tinction thereto the inner element The dispersing lens 33,in accordance with the invention, may preferably be constructed in suchfashion-either by suitable dimensioning of the system elements and theirspacing, or more preferably by correct adjustment of the potentialsthatits focal point coincides with the point of intersection of the rays ofthe condenser system- 28, which point in turn is disposed in or behindthe diaphragm 6. The aperture of the dispersing lens and also itsspacing from the diaphragm are preferably so chosen that the size of thediaphragm aperture is fully utilized.

In Figs. 9-11:

3% is the wall of the tube, i the cathode, 2 the Wehnelt cylinder withthe drawn down control plate 26, 3 and 3 are electrodes forming amongthem the preliminary concentration systems, 6, l and 8 electrodesforming among them the reproducing electron-optical system, 9 and iiithe deflecting plates, 35 and 36 the magnet systems, 31 and 3B poleshoesarranged within the tube, and 62 is the cathode ray.

As shown by Fig. 9, the cathode ray emitted by l is controlled by theuse of ,the plate 26 (the control potential is applied between thecathode i and the plate 26) preliminarily concentrated by the systemcomprising the anode 3, which may consist of a perforated plate withset-on cylinder or may also be constructed in mould-like form, and thehigh-tension anode 3, turned by the field generated by the magnet 35,and projected on to the image screen by the system comprising theelements 6, I and 8, the aperture in the diaphragm i which preferably ismade as small as possible being reproduced on the image screen innatural size or on reduced scale.

In the arrangement according to Fig. 9 the preliminary concentrationsystem comprises the preliminary anode 3 with the set-on cylinder, whichmay be furnished with a comparatively low positive potential (forexample, 300-500 volts), and the anode t, which is connected with alliigh positive potential (for example, 1500-2000 vo ts).

The electron-optical system consists of the two positively biassedplates 6 and 8, between which, in the manner described above, there isarranged the element 1, which is furnished with a negative bias inrelation to the main plates and is constructed, for example, in the formof a cylinder' plate. The distances between i on the one hand and 8 and8 on the other hand should be made as small as possible. In this mannerit is ac? complished that the electronic ray does not vary its speedwhen passing through the system. The described electron system acts asan infinitely thin optical collecting lens.

The plates 6 and 8, if desired, may be united with the plate 4 and theelement 1 with the element 3 to form a structural unit.

A possible form of arrangement and embodiment of the pole shoes 31 and38 and of the magnet 35 is illustrated diagrammatically in Fig. 10.

In the arrangement shown in Fig. 11, the

araaase cathode ray M is first diverted by 180 by the field of themagnet 35-, and then by a further 180 by the field of the magnet 36, sothat its final direction is parallel with its outlet directi on. Ac-'cording to the invention, it is also possible to, arrange thecathode andmagnet fields'in such fashion that the final direction of the cathoderay coincides with the axis of the tube.

In the arrangement according to Fig. 11 ther is end loyed as preliminaryconcentration system a system comprising the preliminary anode 44, themain anode 3, and the element 3, which is arranged between the two andis weakly negative in relation to the preliminary anode.

The potentials of the preliminary concentration system should always beadjusted in such fashion that the electronic ray is preliminary sharplyconcentrated on the aperture in the diaphragm 4,

and the potentials of the electron-optical system should be so chosenthat the same reproduces the diaphragm aperture sharply on the imagescreen.

It has been found to be necessary in the arrangement according to theinvention also to avoid even the slightest action on the cathode ray onits path between the diaphragm and the electron-optical system.According, therefore, to the invention this complete .part of the pathof the ray is screened ofi fully against both magnetic as well aselectrostatic fields of interference by screening means arranged eitherwithin or on the outside of the tube. Such screening means in theirsimplest form consist of an iron or the like tube of /2-2 mm. wallthickness.

The invention is in no way limited to the forms of embodiment quotedmerely by way of example. It is in fact quite possible to employ othersuitable electrostatic preliminary concentratlon or collecting systems.The deviation of the cathode ray may also be performed in suitablemanner as desired.

The tube according to the invention combines the advantages of thepreviously known gas tubes.

(low anode potential, wattless concentrationand control) with those ofthe known high vacuum tubes (great sharpness of the point and lack ofsecondary light caused by slow secondary electrons) without thedisadvantages of these types of tubes.

If desired, the tube according to the invention may be operated with afilling of gas (preferabl as weak as possible).

I claim: Y

1. An electron-optical system for Braun tubes comprisingone'plate-shaped element having an aperture and being adapted to besupplied with a high positive potential, and a second plateshapedelement having an aperture and being furnished at least at its sidefacing the first said element with a metallic cylinder, the diameter ofwhich is considerably greater than the diameter of said aperture, saidsecond element being adapted to be supplied with a lower positivepotential than said first element.

2. An electron-optical system for Braun tubes comprising oneplate-shaped electrode having a 'diameter considerably above 10millimetres, said plate-shaped electrode having an aperture, thediameter of which is in the order of five mm., said electrode beingadapted to be supplied with a high positive potential, and a secondplateshaped electrode having a diameter considerably above 10millimetres, said second plate-shapedelectrode having an aperture, thediameter of nished at its side facing the first said electrode saidelectrode being adapted to be supplied with a high positive potential,and a second plate-shaped electrode having a diameter considerably above10 millimetres, said second plate-shaped electrode having an aperture,the diameter of which is in the order of five mm. and being furnished atits side facing the first said electrode with a metallic cylindersurrounding said aperture, the diameter of said cylinder being in theorder of ten mm., said second electrode being adapted to be suppliedwith a positive potential which is lower than the potential, which thefirst said electrode is to be supplied with, said second electrode beingarranged at a small distance from the first said one, the edge of saidcylinder being spaced from the first said electrode for about one mm.

4. An electron-optical system for Braun tubes comprising threeelectrodes arranged one after another, the first and the third of saidelectrodes consisting of a plate-shaped element having an aperture andbeing adapted to be supplied with a high positive voltage, the secondelectrode consisting of a plate-shaped element having an aperture andbeing furnished at its side facing said third electrode with acylindrical abutment, the diameter of said abutment being about twicethe diameter of said aperture, said second electrode being arranged inclose proximity to said first electrode and near said third electrode.the distance between the plate-shaped element of the second electrodeand the first said electrode on the one hand and the distance betweenthe edge of said abutment and said third electrode on the other handeach amounting to approximately one mm., said second electrode beingadapted to be supplied with a lower positive voltage, the arrangementbeing such that the braking field is mainly restricted to the spacebetween said second and said third electrode.

5. A Braun tube for television purposes comprising an evacuatedenvelope, a cathode and an anode arranged in operative relationshipthereto, said anode having an aperture of small diameter, a picturereceiving screen, deflecting means for deflecting the cathode ray forproducing a scanning of said screen, an electron-optical system forreproducing said anode aperture on said screen, said system beingarranged between said anode and said deflecting plates, and means forparallelizing the cathode ray between said cathode and said aperture,said means including at least one electron-optical collecting lenssystem and at least one electron-optical dispersing lens system.

6. A Braun tube for television purposes comprising an evacuatedenvelope, a cathode and an anode arranged in operative relationshipthereto, said anode consisting of a holding plate of good thermalconductive material and a small disc connected to said holding plate,said disc having a small aperture and consisting of a highly refractorymaterial, means for concentrating the cathoderay on to said aperture, apicture receiving screen, deflecting means arranged between said anodeand said screen and means for reproducing said aperture on said screen.

7. A Braun tube for television purposes comprising an evacuatedenvelope,a cathode and an anode arranged in operative relationship thereto, saidanode aving an aperture, means for concentrating the cathode ray intosaid a-perture, a picture receiving screen, deflecting means fordeflecting the cathode ray for scanning said screen, said deflectingmeans being arranged between said anode and said screen, anelectron-optical system for reproducing said anode aperture on to saidscreen, said electron-optical system including one plate-shapedelectrode being arranged between said anode and said deflecting meansand having an opening the diameter of which is con-,

siderably greater than the diameter of said aperture, said electrodehaving at its side facing said screen a cylindrical abutment, thediameter of which is considerably greater than the diameter of saidopening and the length of which is at least equal to its diameter, saidelectrode being adapted to be supplied with a positive potential, and afurther plate-shaped electrode having an opening which is nearly equalto the opening of said first electrode, said further electrode beingadapted to be supplied with a potential which is higher than that whichthe first said electrode is adapted to be supplied with, said furtherelectrode being arranged between said first electrode and the screen,and a metallic tube having a diameter which is considerably greater thanthe diameter of said opening of said first electrode of saidelectronoptical system, said tube being arranged between said anode andsaid first electrode and being connected to one of these electrodes.

8. Braun tube for television purposes comprising an evacuated envelope,a cathode and an anode arranged in operative relationship thereto, saidanode having an aperture, means for concentrating the cathode rayintosaid aperature,

a picture receiving screen, two pairs of deflecting plates, the platesof each pair being inclined against each other, said deflecting platesbeing arranged between said anode and said screen, an electron-opticalsystem for reproducing said anode aperture on to said screen, saidelectron-optical system including one plate-shaped electrode arrangedbetween said anode and said deflecting means and having an opening thediameter of which is considerably greater than the diameter of saidaperture, said electrode having at its side facing said screen acylindrical abutment the diameter of which is considerably greater thanthe diameter of said opening and the length of which is at least equalto its diameter, said electrode being adapted to be supplied with apositive potential, and a further plate-shaped electrode having anopening which is nearly equal to the opening of said first electrode,said further electrode being adapted to be supplied with a potentialwhich is higher than that which the first said electrode is adapted tobe supplied with, said further electrode being arranged between saidfirst electrode and the screen, and a metallic tube having a diameterwhich is considerably greater than the diameter of said opening of saidfirst electrode of said electron-optical system, said tube beingarranged between said anode and said first electrode and being connectedto one of these electrodes, an auxiliary electrode adapted to besupplied with a high positive potential, said auxiliary electrode beingarranged between said deflecting plates and said picture receivingscreen, and a metallic wall coating commencing near the first electrodeof said electron-optical system and extending for at least eight cm. inthe direction to the screen.

, 9. A Braun tube for television comprising an evacuated envelope, acathode and an I anode arranged in operative relationship thereto,

said anode having an aperture, means for concentrating the cathode rayinto said aperture, a

picture receiving screen, deflecting means tor deflecting the cathoderay for scanning said screen, said deflecting means being arrangedbetween said anode and said screen, an electron-optical system forreproducing said anode aperture onto said screen, said electron-opticalsystem including one plate-shaped electrode being arranged between saidanode and said deflecting means, and having an opening the diameter ofwhich is considerably greater than the diameter of said aperture, saidelectrode having at its side facing said screen a cylindrical abutment,the diameter of which is considerably greater than the diameter of saidopening, said electrode being adapted to be supplied with a positivepotential, and a iurther plate-shaped electrode having an opening whichis nearly equal to the opening of said first electrode, said furtherelectrode being adapted to be supplied with a. potential which is higherthan that which the first said electrode is adapted to be supplied with,said further electrode being arranged between said first electrode andthe screen, and a metallic tube having a diameter which is considerablygreater than the diameter of said opening of said first electrode ofsaid electron-optical system, said tube being arranged between saidanode and said first electrode and being connected to one of theseelectrodes.

10. A Braun tube for television p p ses comprising an evacuatedenvelope, a cathode and an anode arranged in operative relationshipthereto, saidanode having an aperture, means for concentrating thecathode ray into said aperture, a picture receiving screen, two pairs ofdeflecting plates, the plates of each pair being inclined against eachother, said deflecting plates being arranged between said anode and saidscreen, an electron-optical system. for reproducing said anode apertureonto said screen, said electron-optical system including oneplate-shaped electrode arranged between said anode and said deflectingmeans and having an opening the diameter of which is considerablygreater than the diameter of said aperture, said electrode having at itsside facing said screen a cylindrical abutment the diameter of which isconsiderably greater than the diameter of said opening, said electrodebeing adapted to be supplied with a positive potential, and a furtherplate-shaped electrode having an opening which is nearly equal to theopening of said first electrode, said further electrode being adapted tobe supplied with a potential which is higher than that which the firstsaid electrode is adapted to be supplied with, said further electrodebeing arranged between said first electrode and the screen, and ametallic tube having a diameter which is considerably greater than thediameter of said openingoi said first electrode of said electron-opticalsystem, said tube being arranged between said anode and said firstelectrode and being connected to one of these electrodes, an auxiliaryelectrode adapted to be supplied with a high positive potential, saidauxiliary electrode being arranged between said deflecting plates andsaid picture receiving screen, and a metallic wall coating commencingnear the first electrode of said electron-optical system and extendingfor at least 8 centimetres in the'direction to the screen.

diameter, a picture receiving screen; deflecting means for deflectingthe cathode ray tor producing ascanning of said screen, and means forreproducing said anode aperture on said screen, said means including atleast one electron-optical collecting lens system and at least oneelectronoptical dispersing lens system, said collecting and dispersinglens systems being structurally united to form one single element.

12-. A Braun 'tube comprising means ior'proconcentrating system forconcentrating the oathode-ray onto said diaphragm, an image screen, anelectronoptical system for reproducing said diaphragm onto said imagescreen, and means for deviating the path of the cathode ray between saiddiaphragm and said electron-optical system to increase the path of thecathode ray between said diaphragm and said electron-optical system.

13. A Braun tube comprising means for pro-' ducing a cathode ray, adiaphragm, a preliminary concentrating system tor concentrating theoath-- ode ray onto said diaphragm, an image screen, an electronopticalsystem for reproducing said diaphragm onto said image screen, andmagnetic field producers for, deviating the path of the cathode raybetween said diaphragm and said electron-optical system to increase thepath of said diaphragm and said electron-optical system.

15. An electron-optical system for Braun tubes comprising a plate-shapedelectrode having an aperture, said electrode being adapted to besupplied with a high positive potential, and a second plate-shapedelectrode having an aperture of substantially the same size as the firstsaid aperture, said second plate-shaped electrode being furnished at itsside facing the first said electrode with a metallic cylinder,surrounding said aperture in the second said electrode, the diameter ofsaid cylinder being about twice the diameter of said apertures, thediameters of said plateshaped electrodes being substantially larger thanthe diameter of said cylinder, said second electrode being adapted to besupplied with a positive potential which is lower than the potentialwhich the first said electrode is to be supplied with.

16. In a Braun tube more particularly for television purpcses incombination with a diaphragm having an aperture, with means including acathode for producing a bundle of cathode ray to illuminate saidaperture with cathode rays, with a picture receiving screen, and withmeans for electron-optically reproducing said aperture on said screen: apreliminarycathode ray concentrating system mounted between said cathodeducing a cathode ray, a diaphragm, a preliminary and said diaphragm forconcentrating said bundle onto said aperture, and comprising at leastone plate-shaped electrode and a cylindrical electrode mounted betweensaid plate-shaped electrode and said diaphragm, said plate-shapedelectrode beingadapted to be maintained positive in relation to saidcathode; said cylindrical electrode being adapted to be maintainedpofltive in relation to said cathode but negative in relation to saidplate-shaped electrode.

KURT SCHLESINGER.

